Method and apparatus for scrubbing gases

ABSTRACT

A method and apparatus for efficiently scrubbing gases in which gas is discharged into a body of liquid and forced beneath a flat distributor plate disposed well within the liquid. The gas volumetric radial flow rate and liquid head causes a thin, high velocity gas stream to be developed giving a high scrubbing and reaction efficiency.

United States Patent Price METHOD AND APPARATUS FOR SCRUBBING GASESlnventor: Franklin Carr Price, 33 W. l6th St.,

Chicago Heights, Ill. 6041 1 Filed: Aug. 14, 1970 Appl. No.: 63,681

U.S. Cl ..55/95, 55/227, 55/250, 55/255, 55/256 Int. Cl ..B0ld 47/02Field of Search ..55/95, 227, 244, 250, 256, 55/255 1 July 18,1972

[56] References Cited UNITED STATES PATENTS 3,524,631 8/1970 Mare..55/255 X 1,223,684 4/1917 Fleming. ..55/256 1,175,366 3/1916 Lucas..55/256 X Primary Examiner-Howard R. Caine AttorneyWolfe, Hubbard,Leydig, Voit & Osann, Ltd.

[57] ABSTRACT A method and apparatus for efficiently scrubbing gases inwhich gas is discharged into a body of liquid and forced beneath a flatdistributor plate disposed well within the liquid. The gas volumetricradial flow rate and liquid head causes a thin, high velocity gas streamto be developed giving a high scrubbing and reaction efficiency.

8 Claim, 3 Drawing Figures METHOD AND APPARATUS FOR SCRUBBING GASESDESCRIPTION OF THE INVENTION This invention relates generally tocollector apparatus and more particularly to those devices known as gasscrubbers.

The handling of gases generated from cupolas, with their substantialamounts of entrained particular matter, presents a serious problem forthe metallurgical industry. This is particularly true because manyinstallations are relatively small in size and the effective collectionof the particulate matter imposes a potentially large capital investmentand high operating costs. Consequently, many present installations areinadequately equipped, and this of course results in the emission ofoffensive pollutants into the atmosphere.

Gas scrubbers also present substantial maintenance problems because ofthe nature of the particulate matter present in the gases being cleaned.Basically, these problems fall within two categories when the scrubberis used in connection, for example, with a cupola: first, erosionarising from the abrasive action of the high velocity movement of coke,metallic dusts and metallic oxides in the collecting apparatus; and,second, corrosion arising from the acidic solutions formed by thehydrolysis of S and CO which exist due to the use of a reducingatmosphere within the melting zone of the cupola.

Accordingly, it is the primary aim of the invention to provide animproved scrubber for effectively reducing air pollution by beingsuitable for a wide variety of applications including the removal ofparticulate matter, harmful gases and obnoxious odors at high efficiencyfrom large volumes of gas.

An object of the invention is to provide a method and apparatus of theabove kind utilizing natural laws of gas flow to promote the highlyefficient collection of entrained particulate matter from the gas whileat the same time reducing the attendant maintenance problems normallyassociated with such scrubber devices.

Another object is to provide a scrubber of the above character which isrelatively inexpensive to manufacture, set up and maintain, and which isreadily adaptable for use in com nection with existing facilities.

Other objects and advantages of the invention will become apparent uponreading the following detailed description and upon reference to thedrawings, in which:

FIG. 1 is a fragmentary section of a scrubber embodying the invention;

FIG. 2 is a section taken approximately along the line 22 in FIG. 1; and

FIG. 3 is a section taken approximately along the line 3-3 in FIG. 1.

While the invention will be described in connection with a preferredembodiment, it will be understood that I do not intend to limit theinvention to that embodiment. On the contrary, I intend, to cover allalternatives, modifications and equivalents as may be included withinthe spirit and scope of the invention.

Turning to FIG. 1, there is shown the scrubber portion, constructed inaccordance with the invention, of a more extensive gas treatment orcollector system 10. The scrubber portion includes a generallycylindrical tank 11 whose upper gas receiving end 12 is funneled at 13to a nozzle 14 ending in a lower open end 15 disposed generallyhorizontally and approximately in the middle of the tank 11. The lowerend of the tank 11 contains a body of scrubbing liquid 16 whose upperlevel, in the illustrated arrangement, is indicated by the dashed line17. The liquid level is maintained by a pair of overflow headers 18consisting of pipes 19 communicating at upper and lower openings 20 and21, respectively, with the tank 11. Each header 18 has a plurality ofvertically disposed threaded openings 22. Plugs 23 close all but aselected pair of the openings 22, and overflow pipes 24 are connected tothe selected pair of openings to establish the liquid level indicated bythe line 17. Normally, liquid is continuously added to the tank ll inthe form of gas cooling sprays added to the gas stream, indicated by thearrows 25, at an earlier point in the system 10. it will be appreciatedthat, by repositioning the overflow pipes 24 into another selected pairof the threaded openings 22, a different head can be established for thescrubbing liquid.

For driving the gas through the scrubber, an exhaust duct 30 opens at 31into the tank 11 well above the liquid level, and the duct 30 isconnected to a gas driving fan, not shown.

In accordance with the invention, the nozzle end 15 is well beneath thescrubbing liquid level and a distributing plate 35 is secured to thenozzle 14 so as to extend radially therefrom in a generally horizontalplane from the opening 15 so as to define a substantially flat,horizontal surface 36 surrounding the open end 15 beneath which the gasis forced. The gas, at a high volumetric rate, is thus impinged directlyon the liquid surface in an area 37, and the gas then escapes radiallyat the interface between the surface 36 and the liquid. The pressure ofthe liquid head, and the reduced gas pressure resulting from theincreased speed of the gas beneath the surface 36, produces a very thinhigh velocity gas stream passing from the nozzle opening 15 beneath thesurface 36 and thence into the body of the scrubbing liquid. At the edgeof the distributing plate 35, the gas again abruptly changes directionand bubbles upwardly.

It will be noted that since the plate 35 surrounds the nozzle end 15,the gas must flow radially beneath the surface 36 and hence there is notonly a pressure drop resulting from the increased velocity of the gasflow but also the pressure drops as a result of radial expansion of thegas. This causes the liquid surface to closely approach the platesurface 36, constricting the passage through which the gas moves anddefining the thin, high velocity gas stream.

Separation of solids occurs when the gas impinges on the liquid area 37.Further scrubbing action occurs as the very thin stream of gas movesbetween the liquid-surface 36 interface. Still further separation isbelieved to occur as the gas is flung outwardly from the periphery ofthe distributing plate 35 at high velocity.

Preferably, the nozzle end 15 is circular and the distributing plate 35annular. To insure that the plate 35 remains in a substantially flathorizontal relationship, a plurality of tum-buckle fitted support rods41 are connected between the sides of the nozzle 14 and the periphery ofthe plate 35. Access doors 42 in the side of the tank 11 permit the rods41 to be readily extended or shortened to produce the proper dispositionof the plate 35.

To illustrate the action of the plate 35, it has been found that if theplate is not utilized, violent bubbling occurs as gas is forced from thenozzle 14 into the scrubber liquid. When a distributing plate is used,vigorous bubbling occurs in the liquid and, as the diameter of the plateis increased, only frothy bubbling is encountered at the periphery ofthe plate. The diameter of the plate 35 should increase in directproportion to the volumetric flow rate of the gas being handled by theapparatus but good results have been obtained if the diameter of theplate 35 is at least 3% times greater than the diameter of the nozzleopen end 15.

The violence of the bubbling action and the efficiency of the system isalso affected by the liquid head relative to the position of thedistributor plate 35. An increasing head produces better results as thevolumetric flow rate of the gas increases. It is for this purpose thatthe headers 18 are provided since the head can be adjusted for bestresults with a given gas flow.

Solids separated from the gas flow are collected in a tapered bottomportion 45 and preferably are continually removed by, in the illustratedconstruction, an auger conveyor 46. A removable lower door 47 permitsperiodic cleaning of the scrubber. A funnel-like skirt 48 mounted withinthe tank 11 beneath the plate 35 directs solids downwardly into thescrubbing liquid body and minimizes the amount of material carried uparound the skirt 48 to the overflow pipes 24.

To minimize agitation or wave action at the liquid surface, a stabilizerin the form of a cylindrical metal band 49 surrounds the nozzle 14 andextends through the upper surface of the scrubber liquid.

To minimize the amount of water carried away by the scrubbed gas, thegas passes from the scrubbing liquid through a cylindrical screen 51 andan annular demister 52 mounted in a ring structure 53 secured within thetank. The demister 52 is of the conventional type which includes aplurality of curved plates setting up a spiraling motion in the gasstream tending to separate, by centrifugal force, liquid entrained inthe gas flow. The screen 51 collects large liquid particles and createsminor disturbances in the gas stream so as to further separate liquidfrom gas being taken from the tank 11. It will be noted that the exhaustduct 30 is positioned to assist the swirling flow of gas through thedemister.

For insuring proper start-up action, a baffle plate 55 is positionedbeneath and over the open nozzle end 15. The plate 55 insures that, uponinitial gas flow, there is no initial violent bubbling or gushing of thegas from the nozzle 14. As soon as the gas flow is established along theplate 35, the inherent resulting pressure reduction insures properoperation of the scrubber.

It can be seen that substantially only the surface 36 is contacted byhigh velocity gases carrying particulate matter and, even at this pointin the arrangement, many of the particles have been removed byimpingement of the gas on the liquid area 37. Thus, corrosion andabrasion effects are minimal in the disclosed arrangement. Those skilledin the art will appreciate that the addition of neutralizing compoundsinto the scrubber liquid will help control corrosion by reducing the pHfactor. Also, suitable solvents or condensing liquids can be added tothe liquid to neutralize or remove obnoxious gases. The very thin streamof gas moving beneath the surface 36 insures a good contact and highreaction efficiency between the scrubber liquid and virtually all of thegas passing through the system 10.

Iclaim as my invention:

1. In a gas scrubber, the combination comprising, a tank for containingscrubber liquid, a gas inlet nozzle mounted in said tank with a loweropen end disposed generally horizontally near the center of the tank,means for establishing a scrubber liquid level in said tank above saidnozzle open end, said tank having a gas exhaust opening above the liquidlevel, and a distributing plate secured to said nozzle at said open endand extending radially therefrom in a generally horizontal plane so asto define a surface surrounding said nozzle open end beneath which gasmust flow from the nozzle to escape into the liquid.

2. The combination of claim 1 in which said open end is circular andsaid plate is flat and annular, the combination including adjustablesupports for said plate facilitating horizon- I surface of the scrubberliquid, and a conveyor at the bottom of said tank for removing settledsolid matter from the tank.

7. The method of scrubbing a gas comprising the steps of discharging thegas at a high volumetric rate into a body of scrubber liquid, andforcing the gas beneath a substantially flat horizontal surface prior toreleasing the gas for upward bubbling movement from the liquid, theinterface between said surface and said liquid being thus separated by athin, high velocity stream of gas.

8. The method of claim 7 including the steps of controlling thethickness and velocity of said stream by adjusting said volumetric rateand the head of scrubber liquid above said surface.

2. The combination of claim 1 in which said open end is circular andsaid plate is flat and annular, the combination including adjustablesupports for said plate facilitating horizontal alinement of the plate.3. The combination of claim 2 in which the diameter of the Plate is atleast 3 1/2 times greater than the diameter of said open end.
 4. Thecombination of claim 1 in which said means permits adjustment of theliquid level above said nozzle open end.
 5. The combination of claim 1including a baffle plate secured to said nozzle and spaced below saidopen end.
 6. The combination of claim 1 including a wave arrestor bandsurrounding said nozzle and extending through the upper surface of thescrubber liquid, and a conveyor at the bottom of said tank for removingsettled solid matter from the tank.
 7. The method of scrubbing a gascomprising the steps of discharging the gas at a high volumetric rateinto a body of scrubber liquid, and forcing the gas beneath asubstantially flat horizontal surface prior to releasing the gas forupward bubbling movement from the liquid, the interface between saidsurface and said liquid being thus separated by a thin, high velocitystream of gas.
 8. The method of claim 7 including the steps ofcontrolling the thickness and velocity of said stream by adjusting saidvolumetric rate and the head of scrubber liquid above said surface.